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461.
Sulolit Pradhan Lauren E. Brown Joseph P. Konopelski Shaowei Chen 《Journal of nanoparticle research》2009,11(8):1895-1903
Janus nanoparticles were prepared by taking advantage of interfacial ligand exchange reactions of hydrophobic hexanethiolate-protected
gold nanoparticles with hydrophilic 2-(2-mercaptoethoxy)ethanol (MEA). A monolayer of the particles was first formed at the
air–water interface by the Langmuir technique and then deposited onto a substrate surface by the Langmuir–Blodgett method.
The particle monolayer was then immersed into an aqueous solution of MEA for different periods of time. It was found that
the exchange reactions occurred but were limited only to the top face of the nanoparticles and the reaction reached equilibrium
in about 8 h. The resulting particles exhibited amphiphilic characters as confirmed by contact angle and UV–visible, FTIR
and NMR spectroscopic measurements. Of these, the structural discrepancy between the Janus nanoparticles and bulk-exchanged
particles was clearly manifested, in particular, by NOESY NMR measurements. 相似文献
462.
Pierluigi Colli Philippe Laurençot Ulisse Stefanelli 《Continuum Mechanics and Thermodynamics》2000,12(6):423-433
This note deals with a well-posed one-dimensional initial-boundary value problem related to the Frémond thermomechanical model
of structural phase transitions in shape memory materials. The long-time behavior is investigated and it is proved that the
limit set in a suitable topology only contains stationary states.
Received July 06, 2000 相似文献
463.
Loubna A. Hammad Guangxiang Wu Marwa M. Saleh Iveta Klouckova Lacey E. Dobrolecki Robert J. Hickey Lauren Schnaper Milos V. Novotny Yehia Mechref 《Rapid communications in mass spectrometry : RCM》2009,23(6):863-876
The difference in serum phospholipid content between stage‐IV breast cancer patients and disease‐free individuals was studied by employing a combination of chemometric statistical analysis tools and mass spectrometry. Chloroform‐extracted serum samples were profiled for their lipid class composition and structure using precursor ion, neutral loss, and product ion tandem mass spectrometric (MS/MS) scanning experiments. Changes in the relative abundance of phospholipids in serum as a consequence of cancer progression, measured through electrospray ionization (ESI) mass spectrometry of flow‐injected serum samples collected from 25 disease‐free individuals and 50 patients diagnosed with stage‐IV breast cancer, were statistically evaluated using principal component analysis (PCA), analysis of variance (ANOVA) and receiver operating characteristic (ROC) analysis. Lipids whose abundance changed significantly as a consequence of cancer progression were structurally characterized using product ion spectra, and independently quantified using precursor ion scan experiments against an internal standard of known concentration. Phosphocholine lipids that displayed a statistically significant change as a consequence of cancer progression were found to contain an oxidized fatty acid moiety as determined by MS3 experiments. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
464.
Lauren M. Burcaw Paul T. Callaghan 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2009,198(2):167-173
We present a new method for observing fluid diffusion in a porous medium. The method employs 2D exchange spectroscopy for molecules diffusing in the presence of local magnetic field inhomogeneities, in our case distilled water in various sized glass bead packs. Our experiment involves an acquisition and evolution time domain with the two Fourier domains corresponding to the spectral distribution of local fields. We show that exchange in the internal magnetic field can be seen in a 2D spectrum with a characteristic time on the order of that required to diffuse 0.15 sphere diameters with similar behavior found for computer simulations. The method is potentially useful for studying the internal migrations in more complicated systems such as sandstones or other porous media. 相似文献
465.
Lauren L. K. Taylor Imogen A. Riddell Maarten M. J. Smulders 《Angewandte Chemie (International ed. in English)》2019,58(5):1280-1307
Construction of discrete, self‐assembled architectures in water has gained significant interest in recent years as a wide range of applications arises from their defined 3D structure. In this review we jointly discuss the efforts of supramolecular chemists and biotechnologists who previously worked independently, to tackle discipline‐specific challenges associated with construction of assemblies from synthetic and bio‐derived components, respectively. Going forward, a more interdisciplinary research approach will expedite development of complexes with real‐world applications that exploit the benefits of compartmentalisation. In support of this, we summarise advances made in the development of discrete, water‐soluble assemblies, with particular focus on their current and prospective applications. Areas where understanding and methodologies can be transferred from one sector to the adjacent field are highlighted in anticipation this will yield advances not possible from either field alone. 相似文献
466.
The alkane elimination reaction between Salen((t)Bu)H(2) ligands and diethylaluminum bromide was used to prepare three Salen aluminum bromide compounds salen((t)Bu)AlBr (1) (salen = N,N'-ethylenebis(3,5-di-tert-butylsalicylideneimine)), salpen((t)Bu)AlBr (2) (salpen = N,N'-propylenebis(3,5-di-tert-butylsalicylideneimine)), and salophen((t)Bu)AlBr (3) (salophen = N,N'-o-phenylenenebis(3,5-di-tert-butylsalicylideneimine)). The compounds contain five-coordinate aluminum either in a distorted square pyramidal or a trigonal bipyramidal environment. The bromide group in these compounds could be displaced by triphenylphosphine oxide or triphenyl phosphate to produce the six-coordinate cationic aluminum compounds [salen((t)Bu)Al(Ph(3)PO)(2)]Br (4), [salpen((t)Bu)Al(Ph(3)PO)(2)]Br (5), [salophen((t)Bu)Al(Ph(3)PO)(2)]Br (6), and [salophen((t)Bu)Al[(PhO)(3)PO)](2)]Br (7). All the compounds were characterized by (1)H, (13)C, (27)Al, and (31)P NMR, IR, mass spectrometry, and melting point. Furthermore, compounds 1-3 and 5-7 were structurally characterized by single-crystal X-ray diffraction. Compounds 1-3 dealkylated a series of organophosphates in stoichiometric reactions by breaking the ester C-O bond. Also, they were catalytic in the dealkylation reaction between trimethyl phosphate and added boron tribromide. 相似文献
467.
Bermingham MJ Cloke FG Gardiner MG Hitchcock PB Wise LE Yates BF 《Dalton transactions (Cambridge, England : 2003)》2005,(7):1157-1158
The first structurally authenticated 4-azapentalenyl complexes are reported, along with DFT studies, that reveal tendencies for their cyclopentadienyl isostructural nature and an ability to exhibit binding modes of varying hapticity. 相似文献
468.
The module of splines on a polyhedral complex can be viewed as the syzygy module
of its dual graph with
edges weighted by powers of linear forms. When the assignment of linear forms to
edges meets certain conditions,
we can decompose the graph into disjoint cycles without changing the isomorphism
class of the syzygy module. Thus we can use this decomposition to compute the
homological dimension and the Hilbert series of the module. We provide alternate
proofs of some results of Schenck and Stillman, extending those results to the
polyhedral case. We also provide examples which illustrate the role that geometry
plays in determining the syzygy module. 相似文献
469.
The large time behavior of zero-mass solutions to the Cauchy problem for the convection–diffusion equation is studied when q>1 and the initial datum u0 belongs to and satisfies . We provide conditions on the size and shape of the initial datum u0 as well as on the exponent q>1 such that the large time asymptotics of solutions is given either by the derivative of the Gauss–Weierstrass kernel, or by a self-similar solution of the equation, or by hyperbolic N-waves. To cite this article: S. Benachour et al., C. R. Acad. Sci. Paris, Ser. I 338 (2004). 相似文献
470.
Wolf LK Gao Y Georgiadis RM 《Langmuir : the ACS journal of surfaces and colloids》2004,20(8):3357-3361
We present results of the first systematic study on in situ sequence-dependent kinetics for short single-strand oligonucleotide surface immobilization. By measuring film coverage for both thiolated and nonthiolated homo-oligomers as a function of adsorption time, we determine the relative contribution of specific thiol-surface and nonspecific DNA-surface interactions to the overall mechanism of DNA-thiol attachment to gold. We find that sequence-dependent nonspecific surface interactions play a significant role in DNA-thiol immobilization, influencing not only the kinetics but also the extent of oligomer adsorption. For example, sequences that initially form strong, rapid nonspecific contacts with the surface hinder long-time thiol adsorption (i.e., poly(dA)-thiol). In contrast, sequences with nucleotides that initially bind slowly and weakly to the surface (i.e., poly(dT)-thiol) do not obstruct further thiol adsorption, resulting in higher film coverage and Langmuir immobilization kinetics. This view of the DNA-thiol immobilization mechanism is further supported by sequence-dependent rinsing losses observed for thiolated DNA strands but not for analogous nonthiolated strands. Nonthiolated strands contact the surface strongly in a more horizontal orientation, whereas thiolated strands attain a more upright orientation that allows vertical DNA-DNA base-stacking. The results clearly illustrate the importance and interplay of competitive specific and nonspecific forces in forming DNA-thiol films. The specific coverage attained and the time dependence of the adsorption process depend on the prevailing sequence composition. 相似文献